Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a program, and more particularly relates to those used for suitably improving a quality of an image.
Description of the Related Art
For example, image processing for improving a quality of an image includes resolution conversion (image enlargement), noise reduction, and high dynamic range imaging (HDR imaging). These types of image processing include processing using a pixel adjacent to an input pixel which corresponds to a pixel to be output. These types of image processing further include processing of searching for an image area similar to an area including an input pixel corresponding to a pixel to be output and a pixel adjacent to the input pixel, and using an image of the found image area. The processing of searching for the image area similar to the area including the input pixel corresponding to the pixel to be output and the pixel adjacent to the input pixel may be performed only with an image within an apparatus or may be performed with an image in an external server. The image within the apparatus includes input images, images of past frames, and stored images within the apparatus.
For example, image enlargement by a Bicubic method and noise reduction by unsharp mask involve image processing using an input pixel corresponding to a pixel to be output, and a pixel adjacent to the input pixel. On the other hand, as the image processing, searching for and using an image area similar to an area including the input pixel corresponding to the pixel to be output, and the pixel adjacent to the input pixel is also available. Such image processing includes noise reduction through Non-Local Means described in Satoshi Kawata et al., Random Noise Removal Technology to Realize High-Quality Digital Cameras, Toshiba Review Vol. 65, No. 9 (2010) and its improved version, and learning-based superresolution processing (or database (DB) type superresolution processing) described in Hideki Komori, the Journal of the Institute of Image Information and Television Engineers, Vol. 63, No. 10, pp. 1400 to 1402 (2009).
The following technique has been disclosed in Japanese Patent Application Laid-Open No. 2008-199587, as a method for converting a resolution with superresolution. Specifically, by the technique disclosed in Japanese Patent Application Laid-Open No. 2008-199587, an image similar to an input low resolution image is searched for and acquired not only from images in an apparatus but also from stored images in a server on the Internet, as a reference image.
However, the image processing using the input pixel corresponding to a pixel to be output, and the pixel adjacent to the pixel might fail to sufficiently improve the image quality.
Further, the method of searching for the image area similar to the area including the input pixel corresponding to the pixel to be output, and the pixel adjacent to the input pixel from an image in the apparatus has the following problem. Specifically, as described in Yen-wei Chen, Learning-based image quality improvement, Image restoration, and superresolution technique, O plus E, 32(3), pp. 270 to 274, 2010-03-00, Advanced Communication Media, the image quality cannot be sufficiently improved when the found image area is not similar to the area to be output.
Furthermore, the technique disclosed in Japanese Patent Application Laid-Open No. 2008-199587 involves a process of searching for an image similar to the input image in the server on the Internet, even when an image with a sufficient quality can be obtained by the image processing using an image in the apparatus. In other words, the search on the Internet, which takes a long time, is performed even when it is unnecessary. Furthermore, the image quality obtained as a result of the image processing using the image searched on the Internet is not evaluated. Thus, whether a sufficient image quality has been obtained cannot be determined, and an image with an insufficient quality might be output.